Almost every driver living in the temperate zones of the world knows the value of the use of tire chains or other such devices on the wheels of a vehicle when the roads are either icy or covered with snow. However, the installation of tire chains has traditionally been such an ordeal that many drivers prefer either to "take their chances", or else to resort to the rather small, traction increasing devices that are strapped around the tire at two or so locations. These latter devices cannot be used, however, in instances in which solid wheels are involved, for these latter devices have straps that must be threaded through the face of the wheel in order to attach these anti-skid devices.
Snow tires are very popular with a large segment of the driving public, but there are times that snow tires do not suffice, such as in very heavy snow, or when the roads are icy. Although tire chains are indispensable in these latter instances, most drivers postpone the installation of tire chains until they are already threatened with the problem of an immobilized vehicle, but by that time the vehicle may be so near a snowbank or a curb as to greatly complicate the installation of the tire chains.
A careful consideration of the prior art devices reveals that the previous patentees failed to compensate for changes of tire configuration during dynamic conditions, when the vehicle utilizing the tires was underway on snow or ice. More particularly, each portion of a tire at a given moment necessarily becomes wider or bulges during the brief instant of time that it is in contact with the ground. Moreover, there is a definite foreshortening of the radius of the tire at the location between the center of rotation of the wheel, and the point of ground contact. The foreshortening of tires during dynamic conditions is recognized in several publications, and as an example, foreshortening as noted by Firestone Tire and Rubber Company in one of their publications may be reproduced as follows:
______________________________________ Tire Size Overall Diameter Static Loaded Designation (inches) Radius ______________________________________ P155/80R13 22.76 10.15 P165/80R13 23.39 10.39 P175/70R13 22.68 10.12 P175/80R13 24.02 10.62 P185/70R13 23.23 10.33 P185/80R13 24.65 10.86 P175/75R14 24.33 10.86 P185/70R14 24.25 10.83 P185/75R14 24.96 11.10 P195/70R14 24.80 11.04 P195/75R14 25.51 11.31 P205/75R14 26.14 11.54 P215/75R14 26.69 11.75 P205/75R15 27.13 12.04 P215/75R15 27.68 12.24 P225/75R15 28.31 12.48 P235/75R15 28.86 12.69 ______________________________________
There is a difference between the static loaded radius and the dynamically loaded radius, but that distinction is not of particular consequence to my invention.
By selecting for a particular tire, the overall diameter, and by adding to one half of that value, the static loaded radius selected from the table for that particular tire, one is able to ascertain what the loaded height is for that tire under conditions of average, normal conditions. Then, by subtracting the loaded height from the overall dimension (diameter) of the tire at a location 90 degrees away from the ground contact location, the extent of the foreshortening can be determined.
This type of calculation is of particular consequence in a tire equipped with an anti-skid device of the prior art having only two points of contact with the tire tread, such as the Heuneman Pat. No. 2,820,501. It is to be realized that the foreshortening of the tire when one of such tire cleats is in contact with the ground may well mean that the cleat located at the opposite side of the tread may well be dislodged from proper contact, and be flung off the wheel.
A two point of contact device utilizing the rim as a connection point would be dislodged due to the sidewall bulging of the tire at the point of ground contact, therefore precluding this type of device as a satisfactory solution to the problem of designing an easily attached, highly satisfactory anti-skid device.
Some patentees have sought to overcome such disadvantages by utilizing an anti-skid device having more than two points of tire contact. Although the Worthing Pat. No. 2,174,345 teaching an anti-skid device having three points of tire contact would probably not be flung off as readily, it nevertheless fails to take into consideration the fact that some type of compensation for the changes of tire configuration during dynamic conditions must be made. More particularly, inasmuch as Worthing does not create a substantially rigid plane alongside the tire, the cleat portions of the tire can gradually work loose during driving conditions, with the result that the Worthing device will also be flung off, and the patentee's statements to the effect that tensioning of the device to be supported by the tire only are to no avail. This is because the bulging of the tire coupled with the foreshortening of the tire, as shown by the tire loaded height, will cause the tension plane to relax, and the Worthing device to become disconnected and fall off.
The Strapko et al Pat. No. 3,437,121 clearly does not compensate for tire dynamics, at which time the tire foreshortens, so nothing therefore prevents a constant flexing of his device from taking place. Unfortunately in the case of that patentee's device, the turnbuckle utilized in his FIG. 2 may easily loosen during this flexure, and likewise there is nothing to prevent the alternative latching means illustrated in Strapko's FIG. 4 from loosening and permitting his traction device to entirely fall off. It is to be realized that the equivalent of both of these systems was tested by the present inventor, and both were found inadequate.
In effect Worthing and certain other patentees fail to recognize the need for their tire engaging members to flex in a closely controlled manner during dynamic conditions, while being supported from a substantially rigid plane located parallel to the tire, and closely adjacent thereto.
The Deland Pat. No. 4,529,023 apparently overcame the distinct disadvantages of the Worthing device by using a central, rigidly affixed pivotal support member that ostensibly created a rigid plane by the use of an apparently satisfactory tightening device. Unfortunately, the apparent advantages of the Deland device may not be realized in a dynamic circumstance, for each time one of his tread-contacting members comes in contact with the ground, the tire necessarily foreshortens, and serves to loosen the rigid plane the patentee was seeking to establish. In other words, Deland's device did not teach any compensation for the foreshortening that must occur when a tire is exposed to dynamic condition, and if Deland endeavored by his design to clamp the tire engaging members so tightly during the installation procedure as to avoid undesirable loosening, it would require either a person of enormous strength, or else a piece of power equipment in order to accomplish the requisite tightening of the flexible linkages that would bring about the extremely tight gripping of the tire that was needed.
It is for reasons such as these that I was inspired to evolve the present, readily installed anti-skid device, featuring a rigid plane adjacent the tire, upon which are mounted anti-skid cleats for gripping the tire tread in at least three locations, with my highly advantageous arrangement automatically accomplishing the needed compensation for the foreshortening of the tire that necessarily occurs during dynamic conditions of tire use on a vehicle.